In recent years, needs of flat panel displays have been growing with realization of advanced information society. Examples of flat panel displays include liquid crystal displays (LCDs), which are non-self-emitting displays; and plasma displays (PDP), inorganic electroluminescence (inorganic EL) displays, and organic electroluminescence (hereinafter also referred to as “organic EL” or “organic LED”) displays, which are self-emitting displays.
Among such flat panel displays, organic EL displays have particularly received attention because of their capability of self-light emission. In organic EL displays, there are known techniques such as a technique of displaying moving images by passive-matrix drive and a technique of displaying moving images by active-matrix drive that uses thin film transistors (hereinafter abbreviated as “TFTs”). In known organic EL displays, pixels that emit red light, green light, and blue light are placed side by side as one unit, and various colors such as white are produced to perform full-color display.
Such organic EL displays are generally realized by a method in which a red pixel, a green pixel, and a blue pixel are formed by selectively coating organic light-emitting layer materials by shadow mask deposition. However, this method poses problems concerning processing accuracy of a mask, alignment accuracy between a mask and a substrate, and an increase in the size of a mask.
In particular, in the field of large-size displays such as the field of televisions, the substrate size has been increasing from so-called G6 generation (1800 mm×1500 mm) to G8 generation (2460 mm×2160 mm) and G10 generation (3050 mm×2850 mm). In known production methods, a mask having a size equal to or larger than the substrate size is required and thus a mask corresponding to a large-size substrate needs to be produced and processed.
However, since such a mask is composed of a very thin metal film (typical thickness: 50 nm to 100 nm), it is difficult to produce and process a mask corresponding to a large-size substrate. When the processing accuracy of a mask and the alignment accuracy between a mask and a substrate are decreased, different light-emitting layer materials are mixed, which causes a color mixture of emitted light between pixels. To prevent such a phenomenon, the width of an insulating layer disposed between the pixels needs to be increased. However, when the area of a pixel is fixed, the area of a light-emitting portion is decreased. That is, the aperture ratio of the pixels decreases, which decreases the luminance of organic EL elements, increases the power consumption, and shortens the life of organic EL elements.
In known production methods, a deposition source is disposed below a substrate and an organic layer is formed by depositing an organic material from a lower position toward an upper position. Therefore, when the sizes of a substrate and a mask are increased, flection is caused in the central portion of the mask. Such flection of the mask may cause the above-described color mixture of emitted light. In an extreme case, a portion in which an organic layer is not formed is formed and thus leakage is generated between upper and lower electrodes. Also in known production methods, such a mask is degraded and becomes unusable after certain numbers of uses. Therefore, an increases in the size of the mask leads to an increase in the production cost of displays.
To solve these problems, there has been proposed an EL element including an organic EL material unit that emits light in a blue region to a blue-green region; an organic EL material unit that emits light in an ultraviolet region; a fluorescent material unit that emits red light by using, as excitation light, the light in a blue region to a blue-green region emitted from the organic EL material unit; a fluorescent material unit that emits green light by using, as excitation light, the light in a blue region to a blue-green region; and a fluorescent material unit that emits blue light by using, as excitation light, the light in an ultraviolet region (e.g., refer to PTL 1). This EL element can be easily produced compared with the organic EL element produced by the above-described shadow mask patterning method and thus is excellent in terms of cost.
There has been also proposed an organic EL element including an EL light emitting element unit and a fluorescent layer, in which, by disposing a reflective film on the side surfaces of the fluorescent layer, light that travels toward the side surfaces can be efficiently output from the front (e.g., refer to PTL 2).
There has been also proposed a color display apparatus including a light source that emits light having an emission peak wavelength of 400 nm to 500 nm, a liquid crystal display element, and a wavelength conversion unit constituted by a fluorescent body in a combined manner (e.g., refer to PTL 3, PTL 4, and NPL 1). According to the description in PTL 3, since light is emitted from R, G, B fluorescent layers disposed outside a liquid crystal layer, the light utilization efficiency is high and thus a bright color display apparatus can be realized.